The present invention relates to cables, and an apparatus and methods for making cables, that can include at least one optical fiber.
Fiber optic cables include at least one optical fiber that can transmit telecommunication information, for example, voice, data, and video information. Self-supporting fiber optic cables are designed for aerial applications and typically include a messenger wire and a core section having conductors therein that may be solely optical or a combination of optical and electrical conductors. Self-supporting fiber optic cables of the FIG. 8 type may be characterized into two general categories, namely, self-supporting cables with a core section having no excess length relative to the messenger wire, and self-supporting cables having a core section having an over-length, typically about 0.2%, relative to the messenger wire. Examples of self-supporting cables having no core section over-length are disclosed in U.S. Pat. No. 4,449,012, U.S. Pat. No. 4,763,983, U.S. Pat. No. 5,095,176, and U.S. Pat. No. 5,371,823. Examples of self-supporting cables having a core section over-length are disclosed in U.S. Pat. No. 4,662,712 and U.S. Pat. No. 4883671.
When installed in a self-supporting application, self-supporting cables may experience a high degree of tension. The messenger wire bears most of the tension, thereby supporting the core section, and protecting the optical fibers in the core section from high tensile forces. As tension acts on the messenger wire, however, the messenger wire tends to elongate, which results in an elongation of the core section. Elongation of the core section of a self-supporting fiber optic cable not having an over-length may cause attenuation losses and/or can compromise mechanical reliability of the optical fibers. On the other hand, where the core section of a self-supporting-cable having a core section over-length is elongated, the elongation is, up to the amount of existing over-length of the core section, advantageously taken up by the over-length in the core section whereby the core section may be elongated without potentially causing strain and/or attenuation in the optical fibers.
The extruder cross-head used to manufacture self-supporting cables can be configured to define continuous or intermittent webs for connecting cable sections, for example, as disclosed in U.S. Pat. No. 4,467,138. Web-forming extruder cross-heads include a single plunger, e.g., as is disclosed in JP-46-38748 and JP-8-75969. As disclosed in JP-8-75969, for example, the extruder head includes a melt cavity with a molten jacketing material therein. As the messenger wires and core translate through the melt cavity they are coated with the molten jacketing material. As the messenger wires and core exit the extruder head, a die orifice determines the peripheral shape of the cable jacket therearound, and the orifice includes a web-forming area for the formation of webs. The plunger operates by moving into a blocking position in the die orifice between cable sections, physically blocking the molten jacketing material from forming the web. The plunger is reciprocated in and out of the blocking position so that the webs are formed intermittently, spaced by longitudinal gaps.